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Diameter Calculation Using Controllogix

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Thank you for replies and good suggestion to solve my problem. I try to run the line and I get 100 MPM with good stability. Using your formula, the diameter calculation close to actual diameter, just difference about 7-8% because the line speed I get from another casting roll (the section is casting roll - cooling - pull roll #1 - treater - pull roll #2 - winder)but this is enough to scale the diameter from core to full roll. I used following formula: Winder_Ref = (Dancer_Trim_Pct * Line_Spd_ref) / Build_Up Build_Up = Diameter_Calc / Core_Dia (core = 94 mm, full roll = 850 mm) The Dancer control are using PI block with Kp=0.7, Wld=0.03. The input is from dancer_pos_fdbk. I use Scurve (SCRV) to ramp dancer pos fdbk. LIne speed accel and decel is 100 MPM / sec. I run the line with 100 MPM and build up ration increase to arround 2.3 and I try to increase line speed to 120 MPM, the dancer start to oscilate from minimum to maximum position. I try to adjust the PI Kp and Wld but not help, I try to decrease the line speed to 80 MPM and the problem is still exist. How to solve this problem? Thank you for any ideas or solution. James

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James, you're going to have to "take me there" to be able to fine tune it further. I need to know more detail about the process. How responsive is your drive to changes in the speed reference? Since you're regulating speed in the PLC, the lower you set the accel and decel rates in the drive, the better it will perform overall, BUT you have to consider all operations of the drive, you don't want to casue faults if a jog mode or some other control will be affected by changing it. With only 8% adjustment range, you should be able to set the P gain very low, and the I gain much lower. I don't use the d term at all for this application. Your symptoms appear to indicate that your PID gains exceed the responsiveness of the drive. I'm not a PID expert, but to manually tune this application I'll set the P gain very low like 0.01 (PLC5) and the I gain to 0. I adjust the P gain very slowly, and watch the process stop and start at various winder diameters. I'll adjust the setpoint to create a disturbance and watch the trend chart as the PV moves toward the SP. I want minimal overshoot, and no more than 2 oscillations. I repeat this process, graudually increasing the P gain until overshoot is minimal. I then back it off a touch until it's a little overdamped. Hope that generalization helps.

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Thank you for the good forum. I try to increase the speed until 170MPM, the dancer pos is still in mid-pos and I adjust the dancer trim to +/- 30%, P gain set to 0.7 and I gain to 0.03. The process is stable, until we the material reached the full roll diameter. During this process, we set the taper to 0%. We need to have + taper, that will deacrese as diameter increase. I use the formula Tension_Demand = Tension_Ref - (Taper_PCT * Diameter_ratio). I use linear taper and 9 point of diameter (From core to full roll). I generate this base on function generator of controllogix. Any idea or comment? Thank you for the suggestion James